In the manufacture of tufted carpet a fibrous nonwoven or woven primary mat, e.g. a spunbonded mat, of more than 2-4 meters in width, is run through a tufting machine and tufted. Normally, this produces a tufted interim product that may be rolled up and put into storage until an order for that type and color of tufted carpet is received for the carpet finishing line. The tufts are held in the carpet primary backing mat only by the friction of the primary backing mat on the strands of yarn penetrating the mat. When the tufting needles penetrate the primary backing mat each needle carries with it two carpet yarn strands forming a tuft or loop beneath the lower surface of the primary backing mat. As soon as tufts or loops are formed, a hook mounted beneath the primary backing mat enter each tuft or loop and hold each tuftor loop to the desired height while the tufting needles are withdrawn to a location above the primary backing mat, then the hooks are withdrawn from the tufts or loops and the primary backing mat is moved to expose the untufted primary backing mat for the next row of tufts or loops to be formed by repeating the above process.
In the tufting process, the tufting machine will either leave the tufts or loops as-is or, on loop pile machines, will pull the strand of the yarn from selected ones of the last tuft or loop some to reduce the size/heights of selected ones of the just formed tufts or loops (the latter being most typical to make textured carpet). During this controlled shortening of selected tufts or loops a desired amount is accomplished by limiting the length of new yarn for the next row of tufts in known manner, thus causing the remainder of the next tuft or loop to be pulled from the previous tuft or loop thereby making the tuft or loop shorter than its original height. Since each tufting needle makes a hole in the primary backing mat large enough for the two strands of yarn and the tufting needle, the hole, after the tufting needle is withdrawn, is larger than desired to properly grip and hold the strands of yarn. If each hole does not close up sufficiently to a smaller size to grip the yarn sufficiently, the momentum of the pulling of the strand of yarn to shorten tufts or loops length will overpull causing loops or tufts to be too short or to completely pop out of the hole. Any of these undesirable tuft or loop defects, if not corrected by costly labor and time, will produce a defect in the finished carpet. Further, a primary backing mat that does grip the yarn strands sufficiently during the tufting process will produce a more accurate carpet face texture.
The tufted interim product is then wound up, transported to storage or a tip shearing line where it is unwound, tip sheared, wound back up, transported again to storage or a carpet finishing line where it is unwound, adhesive is applied and rewound. During these handling steps the tufts are exposed to snags and other forces that can cause poorly gripped yarn strands to pull partially or all of the way out of holes in the primary backing mat, either individually or in groups of two or more in a tuft row since the yarn strands are held in each hole only by the tuft gripping capability of the primary backing mat. A costly problem the carpet industry has in handling the rolls of tufted interim products is that sometimes one or more tufts is contacted by something on the production line or in transit to and from storage that pulls out one or more tufts and ruins the roll, or at least a section of the roll of interim product. This also happens sometimes in the tufting process. This happens with some primary backing mats more than others. Thus there is a need to determine accurately the capability of the primary backing mat to grip the tufts so that this property of the mat can be increased and so that during manufacture of the primary backing mat this property can be checked periodically for process and quality control purposes. Especially for the latter purpose it is important that the test can be performed quickly and with the least labor required.
Tests do exist for measuring the Tuft Withdrawal Force or Grab Strength for finished tufted carpet products, such as ASTM D-1335 or AWTA Test Code T-34, but in the finished carpet the magnitude of force required to remove a tuft is magnitudes higher and is done for a totally different reason, i.e. to determine how well the carpet will resist vacuum cleaners and wear and tear that tends to pull on the tufts. This test is not sufficient for an interim tufted product, and the use of such a test to improve the characteristics of the primary backing for holding tufts in place is sorely needed.
A test for measuring the tuft gripping strength of primary backing mats having no adhesive or binder added after tufting is disclosed in Published Patent Application No. 20070137294. This test requires more steps, including using a tufting machine to tuft a much larger sample of primary backing mat than is necessary for the test, taking more time and material per sample. It has recently also been discovered that the results of that test are less than fully indicative of the tuft gripping strength of the primary backing mats in typical industrial carpet making processes because it requires pulling the tufted loop in a direction opposite to the direction of the yarn pulls on a loop pile tufting machine, the action causing short tuft defects in tufted interim products.